ReactiveX/RxAndroid ? reverse-engineered prompt

Build me an Android library that adds the missing RxJava helpers for Android apps. I want it to make it easy to take an RxJava stream and switch the work back onto the main thread, and also onto any other Android Looper when needed.

Please include a small sample app that shows how to use it in a real Android screen, with one example that does work on a background thread and then updates the UI on the main thread. It should feel simple to drop into an app, with clear usage and a clean build that I can run right away.

If you need to check current Android or RxJava 3 docs while wiring it up, go ahead and look them up online. Keep the code straightforward, well organized, and make sure the examples are easy to follow.